1. Field of the Invention
This invention relates to a method and system for copper plating substrates and, in particular, to the electrolytic copper metallization of silicon wafers using insoluble anodes.
2. Description of Related Art
The demand for manufacturing semiconductor integrated circuit (IC) devices such as computer chips with high circuit speed, high packing density and low power dissipation requires the downward scaling of feature sizes in ultra-large-scale integration (ULSI) and very-large-scale integration (VLSI) structures. The trend to smaller chip sizes and increased circuit density requires the miniaturization of interconnect features which severely penalizes the overall performance of the structure because of increasing interconnect resistance and reliability concerns such as fabrication of the interconnects and electromigration.
At present, such structures use aluminum and aluminum alloys as the metallization on silicon wafers with silicon dioxide (SiO.sub.2) being the dielectric material. In general, openings are formed in the SiO.sub.2 dielectric layer in the shape of vias and trenches which are then metallized forming the interconnects. Increased miniaturization is reducing the openings to submicron sizes (e.g., 0.5 micron and lower).
To achieve further miniaturization of the device, however, it is being proposed to use copper instead of aluminum as the metal to form the connection lines and interconnects in the chip. Copper has a lower resistivity than aluminum and the thickness of a copper line for the same resistance can be thinner than that of an aluminum line. Copper-based interconnects will therefore represent the future trend in the fabrication of such devices.
Copper can be deposited on substrates by plating (such as electroless and electrolytic), sputtering, plasma vapor deposition (PVD) and chemical vapor deposition (CVD). It is generally recognized that a plating-based deposition is the best method to apply copper to the device since it can provide high deposition rates and low tool costs. However, plating methods must meet the stringent requirements of the semiconductor industry. For example, the copper deposits must be uniform and capable of filling the extremely small trenches and vias of the device. The plating process must also be capable of being controlled so that plating upsets are minimized or avoided and must also be compatible with clean room operations. The deposition of copper from acid copper baths is recognized in the electronics industry as the leading candidate to copper plate integrated circuit devices.
Copper electroplating, in general, involves deposition of a copper layer onto a surface by means of electrolysis using a consumable copper electrode or an insoluble anode. In the consumable electrolytic plating process, the copper electrode is consumed during the plating operation and must be replaced periodically during the plating operation. When plating using insoluble anodes, these anodes are not consumed in the plating process and do not have to be replaced. The following description will be directed to the electrolytic plating of copper using insoluble anodes.
Regardless of the method used to deposit copper on the substrate surface impurities may be co-deposited with the copper. In integrated circuit fabrication it is important that impurity particles not be present in the electrolyte but such impurities may result from sludges formed during the plating operation, impure chemicals and the like. As in all processes used to fabricate integrated circuit (IC) devices, it is necessary that such impurities be minimized and most operations are carried out in a clean room. A clean room is basically a room in which the different process steps are performed and dust particles and other impurity particles are maintained below certain levels by the use of filters and other such cleaning devices. It is important that any plating process used for the fabrication of integrated circuit devices be adaptable for use in a clean room and that the process itself minimize the impurity problems inherent in the plating process.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide an improved method and apparatus (system) for electroplating a substrate.
It is a further object of the present invention to provide an improved electrolytic method and apparatus for copper plating a silicon wafer in integrated circuit fabrication using an insoluble anode.
It is another object of the present invention to provide an electrolytic method and apparatus for copper plating a substrate including silicon wafer substrates using an insoluble anode which plating may be performed in a clean room.
It is an additional object of the invention to provide an electrolyte copper plating process having a substantially steady state electrolyte wherein the plating properties of the deposit remain constant.
Another object of the invention is to provide semiconductors and other devices electroplated with copper.
Other objects and advantages of the invention will in part be readily apparent from the following description.